The steroid glucocorticoid is produced by adrenal fasciculata-reticula cells in the adrenal glands, and are secreted in response to an increase in the level of plasma adrenocorticotrophic hormone (ACTH). Glucocorticoids are involved in carbohydrate, protein, and fat metabolism, have been shown to have anti-inflammatory properties, and are hypersecreted during stress. In excess, glucocorticoids have been shown to damage hippocampus, a structure in the limbic system of the brain that is critical to cognitive functions such as learning and memory. See, e.g., Sapolsky, R. M., Ann. N.Y. Acad. Sci. 746:294 (1994); and McEwen, B. S., Ann. N.Y. Acad. Sci. 746:134 (1994). Furthermore, glucocorticoid neurotoxicity and neuroendangerment has been shown to be critical in neural development and aging as well as in neurological diseases related to hippocampal damage. See, e.g., deKloet, E. R., et al., Ann. N.Y. Acad. Sci. 746:8 (1994).
Studies have been conducted to examine the beneficial effects of extract of the leaves of the gymnosphermus tree ginkgo biloba (e.g., EGb 761) on "antistress" activity by lowering corticosterine levels in stressed rat models. See, Rapin, et al., Gen. Pharmac. 25(5):1009 (1994). EGb 761 had previously been shown to have activity in the cardiovascular system (e.g., reduction of platelet adhesion and thrombi growth), central nervous system (e.g., neuroprotective activity), and neurosensory system (e.g., retinal protection). See, e.g., DeFeudis, et al., Ginkgo Biloba Extract (EGb 761): Pharmaceutical Activities and Clinical Applications (Elsevier, Paris, 1991).
It has now been found that ginkgolides are effective at inhibiting membrane expression of benzodiazepine receptors, eg. adrenal benzodiazepine receptors, and that, having this effect, they can be used to inhibit glucocorticoid release.